1. Field of the Invention
The present invention relates to a method for driving a liquid crystal display (LCD), and more particularly to a method for driving an LCD panel employing a dynamic inversion manner.
2. Description of the Related Art
The image quality of LCDs deteriorates due to a flicker phenomenon, which is directly relative to the sensitivity of naked eyes. Thin film transistor LCDs (TFT-LCDs) and super twisted nematic LCDs (STN-LCDs) are now generally used for display apparatuses. Unfortunately, both of them also have flicker problems. In most cases to avoid flicker images, LCDs must be driven in an AC electrical field, because polarity inversion is needed. In LC cells, we find that flicker is mainly caused by the mobile ion charges. Even though a higher frequency AC applied to the LC cells can reduce the flicker phenomenon. But power consumption is dependent on the frequency of the AC electrical field. On the other hand, due to a stray capacitor effect, the center level of driving signals shifts between two consecutive frame periods, so the amplitudes of driving signals are different between the positive polarity and the negative polarity of the LC cells. Therefore, the flicker problem becomes worse.
Now, there are four driving methods of the polarity inversion, described as follows:
1. Frame Inversion
Driving signals are applied to LC cells in the LCD panel in such manner that each pixel of the whole frame has the same polarity during a frame period, as shown in FIG. 1(a). When the next frame period comes, the polarity of each pixel is inverted, as shown in FIG. 1(b).
2. Row Inversion
FIG. 2(a) Shows polarity patterns of driving signals applied to LC cells in the LCD panel using a row inversion. Driving signals are applied to LC cells in the LCD panel in such manner that each pixel in the same row line, e.g., a scanning line, has the same polarity, and each pixel in the adjacent row line has a polarity contrary to one in either the previous row line or the next row line during a frame period. When the next frame period comes, the polarity of each pixel is inverted, as shown in FIG. 2(b).
3. Column Inversion
FIG. 3(a) Shows polarity patterns of driving signals applied to LC cells in the LCD panel using a column inversion. Driving signals are applied to LC cells in the LCD panel in such manner that each pixel in the same column line, e.g., a signal line, has the same polarity, and each pixel in the adjacent column line has a polarity contrary to one in either the previous column line or the next column line during a frame period. When the next frame period comes, the polarity of each pixel is inverted, as shown in FIG. 3(b).
4. Dot Inversion
As shown in FIGS. 4(a) and 4(b), driving signals having polarities contrary to the adjacent LC cells on the row lines and to the adjacent LC cells on the column lines are applied to each LC cell in the LCD panel, and the polarities of driving signals applied to all LC cells in the LCD panel are inverted every frame period.
The aforementioned conventional driving methods of polarity inversion also have flicker problems during the displaying of a specific test pattern. For example, when an LCD panel using a dot inversion method shows sub-pixel test patterns, flickers are generated on the LCD panel. An LCD panel using a row inversion method has flicker defects during the displaying of a horizontal-line test pattern. In other words, all four driving methods will display flicker images under a specific test pattern. A user with sensitive vision is likely to detect the same problem.
Furthermore, Taiwan Patent No. 401,529 discloses a driving method and a driving circuit for a LCD. By adding more signal driving devices to the upper and lower areas of the LCD panel, the LCD panel can only have four polarity patterns, as shown in FIGS. 6(a)–7(b) of the specification. In this configuration of the LCD panel, more non-display space is needed and leads to an increase in manufacturing costs.